Alex's in his heaven, all's right with the world

My tire's max pressure is 51 psi however there's a thing on the tire that says "Never inflate beyond 40 psi on seat bead". What does this mean?

Edit: Thanks everyone, TIL I know nothing about tires. Max PSI does not equal better performance. Now if you'll excuse me I'm going to go and reflect on how I knew so much about cars but knew nothing about tires.